This invention relates generally to agricultural combines used in the harvesting of crops and is particularly directed to an improved cylinder/concave combination for separating grain from the leafy portion of the plant.
A combine is an agricultural vehicle used in the harvesting of crops. The combine is typically self-propelled and is comprised of a forward header assembly and an aft drive and processing section. The header assembly typically is substantially wider than the aft portion of the combine and includes a plurality of spaced corn or row crop heads which are adapted for engaging the crops in removing the grain therefrom. The thus removed grain, in combination with crop residue such as husks in the case of corn harvesting, are then automatically delivered to the aft drive and processing portion of the combine. In addition to housing the source of propulsion, such as a diesel engine, and operator controls, the aft portion of the combine also includes a complicated threshing system for further separating the grain from the crop residue and for off-loading the thus separated grain from the combine into a transport vehicle such as a truck. The crop residue is then exhausted from an aft portion of the combine and deposited in the field being harvested.
Combines typically make use of a rotating cylinder in the early stages of grain-crop residue separation. The cylinder is typically oriented horizontally and transversely to the direction of combine travel and is adapted to receive that portion of the crop which is separated from the plant by the forward header assembly. The rotating cylinder operates in cooperation with a fixed concave structure positioned adjacent to and below the cylinder. The cylinder-concave combination operates to separate the grain from the husk or leafy portion of the plant. The cylinder generally includes a first plurality of spaced raspbars around its periphery and extending the length thereof, while the concave includes a second plurality of stationary, spaced bars generally parallel to the raspbars. The crop is directed to the space between the rotating cylinder and the concave and the action of the rotating cylinder upon the crop as it is engaged by both the rotating cylinder and concave causes the grain bearing portion of the plant, i.e., the cob in corn harvesting, to become separated from the remaining portion of the plant, i.e., the leafy portion. The grain is then subjected to additional processing for further separation, while the crop residue is exhausted from the combine.
The grate-like concave includes a large number of slots, or apertures, therein formed by the aforementioned second plurality of stationary, spaced bars and a plurality of concave cross bars extending between forward and aft portions of the concave. Unfortunately, the combine ingests more than just plant material. Rocks, soil and other debris taken in by the combine tend to inhibit the various threshing operations within the combine, reducing the efficiency of the grain separation process and the amount of grain recovered.
While prior art concaves are disposed about a portion of the rotating cylinder, they are not formed in a circular arc about the axis of rotation of the cylinder. These prior art concaves include linear sections disposed adjacent to their forward and trailing edges, with a circular arcuate section disposed intermediate the leading and trailing linear sections. With the outer raspbars of the rotating cylinder displaced in a circular arc, the raspbars closely track in a generally parallel manner only the intermediate, circular portion of the concave. Adjacent to the concave's linear leading and trailing edges, the displacement between the cylinder's raspbars and the concave is greater and varies with the angular position of the raspbar. Those areas adjacent to the leading and trailing edges of the concave thus do not provide the closely spaced relation between concave and cylinder necessary for efficient threshing of the plant material ingested by the combine. The increased spacing between the leading edge of the concave and the cylinder's raspbars also inhibits the raspbars from directing foreign materials taken in by the combine through the concave. This results in clogging of the apertures in the concave adjacent to its leading edge such as by soil or rocks preventing the grain bearing portion of the crop from being directed through these apertures and separated from the leafy portion of the plant.
In order to prevent foreign material from clogging the concave, some combine manufacturers have increased the rotational velocity of the cylinder in an attempt to force the foreign material through the apertures in the forward portion of the concave and to maintain these apertures open. However, increasing the rotational velocity of the cylinder increases the likelihood of damage to the harvested crop. This damage is caused by increased impact forces as the faster cylinder contacts the separated grain and appears as cracking making the grain more susceptible to infestation and deterioration.
Increasing the rotational velocity of the cylinder also causes more of the crop residue, which is displaced along the concave, to be recirculated by the cylinder rather than being discharged from the aft, upper edge of the concave. Backfeeding of the crop residue, or its recirculation about the rotating cylinder, reduces the combine's capacity to separate the grain from the plant residue resulting in reduced recovered yields and greater likelihood of residue clogging of the concave. Finally, operating the cylinder at increased rotational velocities increases the combine's fuel consumption rate and is thus less fuel efficient.
The present invention overcomes he aforementioned limitations of the prior art by providing a concave for use with a rotating cylinder in a combine for separating grain from the leafy portion of the plant, wherein the concave subtends a circular arc about and in closely spaced relation to the rotating cylinder. The concave includes a plurality of closely spaced linear bars extending along its length as well as a plurality of closely spaced curved intermediate bars extending from forward to aft in the concave which, in combination, form a large number of rectangular apertures within the concave. The linear bars are positioned on an inner portion of the concave so that their exposed inner edges may be cut such as by a boring tool to form a circular arc for closely matching the displacement path of the cylinder's outer raspbars. By more closely conforming the configuration and shape of the concave to the circular arc over which the cylinder's raspbars are displaced, backfeeding of the crop residue, clogging of the concave by foreign materials such as soil and rocks, and damage to the grain caused by high speed impact with the cylinder's raspbars are essentially eliminated.